Oscillator spring composition and method for fabricating an oscillator spring

Abstract

An oscillator spring material comprising a mixture of a host material with an additive in proportions which permit the thermal evolution of the material's elastic modulus to be tuned, e.g. to correct or compensate for other thermal changes in an oscillator system. The additive comprises a crystalline material having an abnormal thermal evolution of elastic modulus. The host material has a normal thermal evolution of elastic modulus. The additive is mixed with the host material before the host material undergoes a phase transformation into its final form. The additive has a phase transformation temperature higher than the host material, so that additive remains in the same state while the host material phase transformation takes place.

Description

TECHNICAL FIELD[0001]The invention relates to a material composition for controlling the thermal evolution of elastic modulus (Young's modulus) and spring stiffness of oscillator springs for precision instruments. In particular it relates to compositions for and methods of making non-magnetically sensitive springs for use in systems where thermal stability is critical to the correct functioning of the system.BACKGROUND TO THE INVENTION[0002]Up to the early twentieth century, knowledge of materials with limited coefficients of expansion was essentially limited to naturally occurring materials, elements or compounds. The advent of atomic science in the early twentieth century brought with it both an emergent understanding of materials at atomic scale and the need for measurement several magnitudes of precision greater than had previously been known. This in turn led to research for new materials, compounds or alloys, which exhibited limited thermal expansion for the purpose of buildin...

AI Technical Summary

Benefits of technology

[0015]Herein, ambient temperature range may be from 5° C. to 40° C. The proportion of additive may be determined empirically, e.g. to compensate for thermal variations in other components in the oscillator system. Indeed, an advantage of the invention is the ability to “tune” the thermal behaviour as required. In practice, the proportion of additive may be no more than 33 mol %, preferably no more than 10 mol %, more preferably no more than 5 mol %.

[0016]In the mechanical oscillator system itself, the balance may be any suitable balance mass for regulating the oscillation of the spring. The balance mass by a monolithic piece of material. In one embodiment, the balance mass may be integrally formed with the spring, e.g. from a single block of the mixture material defined above. For example, the balance mass may be a thickened region retained at an end of the spring during a forming or cutting process.

[0017]Control of the thermal evolution of the spring material may be achieved more precisely if the additive is mixed with the host material at the stage of the creation of the material before it is formed into whatever shape it is destined to take. Here, mixing may mean incorporating (i.e. physically intermixing) the additive within the host material, rather than adding it via a deposition process after the host material has been formed. In another aspect, the invention may thus provide a method of making an oscillator spring, the method comprising: mixing a phase-transformable precursor material with an additive; forming the mixture into a shape for subsequent use; heating the mixture to a temperature that causes the precursor material to exhibit a phase transformation into a host material having a normal thermal evolution of elastic modulus while the additive remains in a non-phase-transformed state, wherein the additive is made from a material having an abnormal thermal evolution of elastic modulus, and wherein the proportion of additive in the mixture is selected to control the thermal evolution of the spring's elastic modulus in an ambient temperature range to provide thermal stability to the spring's oscillation.

[0018]The host material, which may resemble a matrix in which the additive is dispersed, or a body to which the additive is applied may comprise carbon material, e.g. derived from any polymeric, or pitch or polyacrylonitrile (PAN) precursors. The preparation of the matrix or bulk host material may involve a stage where the material (e.g. the precursor material mentioned above) may be of liquid form of such relative viscosity as to allow the introduction of other material or materials into the mixture and allowing for very precise controlling of the proportions and weights required to enable the resulting material to perform according to requirement.

[0019]It has been found that the transformation critical temperature in producing certain new materials allows for the corrective material (i.e. additive) to go unaltered in the transformation process where the critical temperature for the additive material is not exceeded but where the bulk (host) material undergoes a change of phase. This is particularly but not exclusively the case with certain carbon materials derived from precursors where the precursor material undergoes a thermal process in order to derive the final state material.

[0020]In one embodiment, a body of host material having a normal thermal evolution of elastic modulus was coated with an additive material having an abnormal thermal evolution of elastic modulus to modify or change the thermal evolution of the elastic modulus of the combined material in the ambient range. A possible drawback with this embodiment is that it may be difficult to achieve constancy in the deposition thickness of applied material. Furthermore, a significant increase in stiffness may arise as well as an instability in the adherence of the thin additive film to the host material particularly when in mechanical flexion mode and the thin additive film approaches its sigma zero threshold, the point at which its linear elasticity gives way to plastic deformation or fracture. Accordingly, an embodiment in which the additive is mixed within the host material may be preferred.

Problems solved by technology

Up to the early twentieth century, knowledge of materials with limited coefficients of expansion was essentially limited to naturally occurring materials, elements or compounds.

This in turn led to research for new materials, compounds or alloys, which exhibited limited thermal expansion for the purpose of building measuring instruments.

The drawback of these alloys in the modern world (especially their use in balance springs for precision instruments) is their sensitivity to magnetic fields and a change from abnormal (i.e. positive) thermal evolution of elastic modulus to normal (i.e. negative) thermal evolution of elastic modulus in the ambient temperature range.

However, although a change in the sign of the thermal evolution of elastic modulus has been found, consistent manufacturing tolerance has been difficult to achieve and the resultant stiffening of the material has required further compensatory measures.

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